Yeah it is. :[
I haven't encountered too many thankfully. But I think I handled them with Cofagrigus normally. Foul Play hurts though, even with 2 Atk IVs, but it's one of the better mons on the team to take the will-o-wisp.
And I haven't run into ANY Gligar with it. But I can see how it could be an issue. To be honest, overall, Cofagrigus has been the all-star for me.